To protect a wire harness, formed for example by bundling a plurality of electric wires onto the body of an automobile, a wire harness protector is employed. The wire harness protector, a three-dimensional compact of a resin material, holds the wire harness in a prescribed condition and prevents the wire harness from coming in contact with other materials, thereby protecting the wire harness.
Such a wire harness protector can be molded by injection molding into a three-dimensional shape, such as the shape of an automobile body or a wire harness interconnection path.
However, it is relatively difficult and costly to manufacture a large-sized product having a complicated shape, such as the wire harness protector, by injection molding. Large-scale equipment is required, which corresponds to an increase in equipment costs. The design of the metal mold, for a large-sized product, is complicated, with a corresponding increase in the manufacturing cost of the metal mold itself.
On the other hand, numerically controlled (NC) blow molding, a form of resin molding, is advantageously capable of: facilitating three-dimensional molding of an elongated product with a high degree of freedom of design; forming a large-sized product at a low equipment cost, because it requires a smaller machine than that employed in injection molding; employing a metal mold with a low manufacturing cost of a zinc alloy or an aluminum alloy with a molding pressure of about 0.5 to 0.7 MPa, i.e., a pressure about 100 times smaller than the pressure in injection molding; and performing precise molding.
Numerically controlled blow molding has recently been improved, and is capable of suppressing the occurrence of burrs and contributing to the reduction of the manufacturing cost. Numerically controlled blow molding can control the thickness of a parison by adjusting a clearance between a metal mold and a core for properly changing the thickness of the as-obtained molding without varying the metal mold, thus preventing the occurrence of burrs in a multilayer manner, which contributes to the reduction of the manufacturing cost. Numerically controlled blow molding molds different materials through a proper combination of resin materials without varying the metal mold, and, by using insert molding, reduces the numbers of elements and steps needed.